1. Field of the Invention
The present invention relates to a tube-enclosed optical cable containing ribbon units, and more specifically to a tube-enclosed optical cable containing ribbon units which can improve the economical efficiency of the process by simplifying the manufacturing process of optical cable and at the same time can improve the water blocking capability and compression characteristics of optical cable, by providing optical cable characterized by coating particularly the central member of the cable with an absorptive substance and optical cable characterized by inserting interstices coated with an absorptive substance into the empty spaces between one or more tubes encircling the central member and the sheath enclosing the tubes.
2. Description of Prior Art
Optical cables are widely used for transmitting electric and electronic signals in television, computers and telephones, and are getting more and more spotlight since they can transmit a huge amount of information compared with the conventional coaxial cable in particular. But the optical fibers used in such optical cables are very small in diameter, vulnerable to impact and easily damaged by contact especially with moisture. So there has been an acute demand for such an optical cable with a structure that can protect it from moisture and external impact, and accordingly, optical cables having a variety of structures have been developed.
As an example from the prior art, FIG. 1 shows the structure of the optical cable presented in the U.S. Pat. No. 5,229,851. As illustrated in the drawing, the optical cable comprises a central member 10, one or more liquid impermeable tubes 16 encircling the central member in an alternating hand helix at a given distance, one or more ribbon units 14 received loosely in the inside of the tube, and a sheath 20 of a plastic material enclosing the liquid impervious tubes; and to protect optical fiber from moisture and external impact, all the empty spaces between the inner membrane of the sheath and tube and between the tubes are filled with jelly-like water blocking substance 12.
But for actual connection and use of the cables, it is necessary to pull out optical fibers from optical cables. If the jelly-like water blocking substance is filled in the cable, the jelly should be removed as well to pull out the optical fiber. So the drawback is that hands or the equipment can be contaminated from the jelly, and due to the viscosity of the jelly itself, the process of filling it takes a lot of time. This could lead to lowering of the yield rate and economical efficiency of the process in general. And as the jelly may not be filled completely in the empty spaces between tubes, it is a fact that a satisfactory pressure characteristic has not been obtained yet.
Therefore, researches have been continued to make up for such drawbacks, and as a result the optical cable having the structure as shown in FIGS. 2 and 3 has been developed. The optical cables shown in FIGS. 2 and 3 disclosed in U.S. Pat. No. 5,621,841. First, the optical cable shown in FIG. 2, as shown in FIG. 1 above, comprises a central member 10, tubes 16 encircling the central member 10 in an alternating hand helix, ribbon units 14 located in the inside of the tube 16, and sheath 20 encircling the tubes 16. In this optical cable, the spaces between the tubes 16 are filled with waterproof yarns 24, and the tubes 16 are first wrapped with waterproof tapes 22 and then enclosed with sheath 20 of a plastic material.
That is, in the optical cable, by using waterproof tapes wrapping waterproof yarns and ribbons instead of the jelly-form water blocking substance, they have solved the problem arising from using the jelly-form water blocking substance. But the waterproof yarns are consisting of powder or fine thread containing superabsorbent polymer, and in the optical cable such waterproof yarns are exposed to the outside during the cable assembling process. Since the tube could be rubbed against the surface of waterproof yarn, dust could be created. This dust can be a factor of making products defective and impeding the cleanliness in the factory, which is a problem that can cause a lowering of the economical efficiency and yield rate of the process.
Also in the optical cable shown in FIG. 3, the ribbon-type optical cable comprising central member 10, tube 16, ribbon units and sheath 20 is characterized by having a structure wherein waterproof tapes 26 longitudinally wrap around the central member and waterproof yarns fill the empty spaces between the tubes. This also cannot solve the problem arising from the optical cable shown in FIG. 2. Moreover, according to the structure shown in FIG. 3, separate equipment and process are necessary for longitudinal wrapping of waterproof tapes in the cable assembling process. And since waterproof tapes need to be exchanged while working, continuous work becomes difficult, which leads to a lowering of the economical efficiency of the process. And longitudinal wrapping of tapes may create gaps between tapes, which can cause reduction of the water blocking characteristic of the cable.
As a structure for solving the problem of the pressure characteristic reduction and the bending characteristic in the optical cables in FIGS. 2 and 3, there is optical cable by U.S. Pat. No. 6,014,487 that has a structure as shown in FIG. 4. Referring to FIG. 4, the cable in the ribbon-type optical cable comprising a central member 10, tubes 16 filled with jelly-like water blocking substance 12 and ribbon units 14, and sheath 20, is characterized by having a structure wherein interstices 28 are inserted into the empty spaces between tubes 16 for improving the pressure characteristic of the cable, and water swellable members 24 are placed around the interstices 28. By inserting the interstices of a plastic material, the pressure characteristic of the cable can be improved and it can prevent moisture from being absorbed in the cable through water blocking members around the interstices. But since the interstice itself cannot have any water blocking characteristic, a sufficient water blocking characteristic of the cable cannot be obtained. And by using yarn as the water blocking member, dust can be created by yarn during the cable assembling process. And because it becomes necessary to perform complicated work involving simultaneous arrangement of the tubes, interstices and water blocking members, a lowering of productivity becomes another problem.
Due to such problems in prior art, there is an acute demand for the optical cable having a structure that has excellent water blocking and pressure characteristics and which can maximize economical efficiency since the process is simple and does not create contaminating materials.
It is an object of this invention to provide a tube-enclosed optical cable containing ribbon units that has an excellent water blocking characteristic but can be produced by a simple process, and can prevent creation of dust by waterproof yarn, by coating the absorptive substance itself on the central member and forming water swellable members of non-jelly substance between tube twist and polyethylene sheath, in order to solve the problems of the conventional optical cables.
It is another object of this invention to provide a tube-enclosed optical cable containing ribbon units that has excellent pressure and water blocking characteristics but can be produced by a simple process, and can prevent creation of dust from waterproof yarn, by inserting interstices coated with absorptive substance into the empty spaces between tubes and sheath of a plastic material, in the optical cable having the structure.
In accordance with this present invention a tube-enclosed optical cable containing ribbon units comprises a central member with the surface coated with absorptive substance; at least one or more tubes filled with water blocking substance capable of preventing permeation of moisture into the inside, containing at least one or more optical fibers, and encircling the central member at a given distance in an alternating hand helix; a sheath of a plastic material enclosing the tubes; and water swellable members of non-jelly substance formed between the twist of the tubes and sheath to prevent permeation of moisture into the inside of the cable.